Monolithic ceramic, high carbide content powdered metal, cast metal wear resistant alloy and other metallic and non-metallic materials have been considered as wear surfaces for engine valve train tappets, rocker arms and finger followers. In each of these cases the method proposed to attach the wear resistant material to valve train parts has introduced additional piece costs and manufacturing complexity.
The subject of this invention is a workpiece modified to permit attachment of the wear face through the use of a sleeve electromagnetically formed around the workpiece body and wear face so as to firmly attach the two pieces together. This method offers manufacturing process and piece cost advantages over the more conventional braze, solder or adhesive bonding or shrink fitting techniques.
Examples of the prior art can be found in United Kingdom Patent Application No. 2,093,554A and in U.S. Pat. No. 4,366,785.
The basics of the method employed can be found in U.S. Pat. No. 4,261,092.
Factors and features thought to be critical in the electromagnetic forming method when applied to a typical hydraulic tappet body include the physical and mechanical properties of the sleeve, sleeve thickness, diametric differences between the sleeve, tappet wear pad and tappet body, the thickness of the wear pad and the clamping angles on the tappet body and wear pad outside diameter in the sleeve contact zone. This latter feature controls the clamping force normal to the plane of the wear pad face. Electromagnetic forming of the sleeve when ceramic or other brittle material wear pads are employed incorporates the principals described in U.S. Pat. No. 4,261,092 entitled "Method of Electroforming a Metallic Sleeve and Ceramic Shaft Joint".